(1) Field of the Invention
The present invention relates to a tandem axle vehicle suspension system which, in variant embodiments, employs one or two torque beams each supporting an axle of a tandem axle vehicle where a single elastomer spring mounted on the torque beam is subjected to compression and shear forces during over-the-road operation.
(2) Description of the Related Art
A typical tandem axle suspension system of the type provided by the present invention is commonly comprised of a hanger member depending from the vehicle chassis, a load compensator pivotally supported by the hanger member, and independent forwardly and rearwardly extending torque beams each pivotally connected to the load compensator at one end and connected to the vehicle's forward and rearward axles at their opposite ends, respectively. Compressible elastic members are connected between the compensator and torque beams, with the pivotal connections of the torque beams to the compensator causing both compression and shear forces to be applied to the compressible members during over the road operations.
In a variant embodiment of prior art tandem axle vehicle suspensions, only one torque beam is connected to the load compensator for pivoting movement of the beam relative to the compensator. The compensator extends longitudinally in either a forward or rearward direction opposite to the direction that the torque beam extends from the compensator. One of the vehicle axles is mounted on the extended portion of the load compensator and the second vehicle axle is mounted on the distal end of the torque beam from the compensator. In this type of suspension system too, a compressible elastic member is mounted between the compensator and the torque beam and the pivoting movement of the torque beam relative to the compensator causes both compression and shear forces to be applied to the elastic member during over the road operations.
Examples of these prior art tandem axle vehicle suspension systems employing load compensators are disclosed in U.S. Pat. No. 3,471,165 to Raidel, U.S. Pat. No. 3,632,128 to Raidel, and U.S. Pat. No. 5,033,769 to Raidel, all assigned to the assignee of the present invention and incorporated herein by reference.
In tandem axle suspension systems employing a load compensator, the compensator is usually comprised of an inverted U-shaped channel member having a hollow interior. The torque beam or beams are connected for pivoting movement relative to the compensator by a pivot bushing assembly mounted inside the interior of the compensator. The compressible members employed with these suspensions include elastomer springs, air springs, and other conventional types of springs.
Regardless of the type of compression member employed with the suspension system, very often size limitations required that the compressible member be mounted between the compensator and torque beam or beams within the hollow interior of the compensator. The lateral width of the compensator is typically designed Just wide enough to receive one end of the torque beam or beams and the pivot bushing connecting the beam or beams to the compensator. Therefore, it was necessary that the compressible members or springs be designed with a lateral width sufficiently small to insert the compressible member within the interior volume of the compensator between the compensator and torque beam. A typical lateral width of prior art compressible members is 4 inches. However, it has been found that the positioning of the springs in the interior volume of the compensator makes it very difficult to install and remove the springs due to the limited space in the compensator interior. This makes it very difficult to perform maintenance and make repairs to the confined springs. It also makes it difficult to use the same suspension structure for various different load applications because of the difficulty in changing spring sizes in the confined area inside the compensator. Furthermore, due to the lateral size limitations placed on the springs by their being required to be positioned inside the compensator interior volume, the springs are at times inclined to buckle laterally in use. This buckling of the springs could have a detrimental effect on the axles of the vehicle. The size limitations of the springs also limit the maximum load of the vehicle that they can support.
The positioning of the compressible members between the load compensator and torque beam in the interior of the compensator was satisfactory for the compressible members resisting vertical compression forces exerted on the members as a result of pivoting movement of the torque beam or beams relative to the compensator. However, the pivoting movement of the torque beam or beams relative to the compensator also exerted a horizontal shear force on the compressible members especially when braking or accelerating, and additional structure was required to be added to the suspension systems to enhance the ability of the compressible members to resist these shear forces. One method of enhancing the ability of the compressible members to resist shear forces was to add a torque bar connected between the compressible members mounted between the load compensator and the pair of torque beams. This type of suspension system is disclosed in U.S. Pat. No. 3,471,165. However, the addition of the torque bar and its associated structure significantly increased the cost of producing suspension systems of this type and the increased structure also added to the overall weight of the system.
In suspension systems employing a load compensator with forwardly and rearwardly extending torque beams mounted thereto, a third compressible member was added to the suspension system to enhance the ability of the compressible members mounted between the load compensator and the two torque beams to resist shear forces. The third compressible member was typically mounted between a pair of brackets attached to each of the forwardly and rearwardly extending torque beams in an orientation where the third compressible member would be subjected to compression forces in response to pivoting movement of either of the two torque beams relative to the load compensator. An example of a tandem axle suspension system employing a third compressible member is disclosed in the U.S. Pat. No. 3,632,128. However, this solution to resisting shear forces also required not only the addition of the third compressible member but its associated structure connecting the third compressible member to the two torque beams. The addition of the third compressible member and its associated structure to the suspension system significantly increased the cost of producing the system and also added to the overall weight of the suspension system.
The solutions developed for resisting shear forces exerted on compressible members discussed above were not adaptable to the tandem axle suspension system of the type employing a load compensator with one of the vehicle tandem axles mounted to the compensator and a single torque beam mounted to the compensator with the second of the vehicle tandem axles mounted to the torque beam. In these types of suspension systems, in order to enhance the ability of the compressible member to resist shear forces, a secondary compressible member was mounted between the load compensator and the torque beam. This secondary compressible member was typically oriented at an angle relative to the primary compressible member mounted between the torque beam and load compensator so that the secondary compressible member was subjected to only compression forces as a result of the pivoting movement of the torque beam relative to the compensator. However, the addition of the secondary compressible member to this type of suspension system also required the addition of structure to orient the secondary compressible member in its optimum position relative to the load compensator and torque beam to resist shear forces on the primary compressible member. The addition of the secondary compressible member together with its associated structure again increased the overall cost of production of the suspension system and added to the overall weight of the suspension system.
What is needed to improve existing tandem axle vehicle suspensions employing a load compensator mounting either one torque beam or a pair of torque beams is an arrangement of the connection of the compressible member between the load compensator and the torque beam or beams where the total number of compressible members employed in the suspension system is reduced and the structure associated with the suspension system compressible members is also reduced, thereby reducing the overall cost of producing the suspension system and the weight of the suspension system. What is also needed is a mounting of a compressible member between a torque beam and load compensator where the compressible member is exposed and easily accessible, thereby enabling adjustments to be made to the suspension system to suit it to a variety of load applications by simply changing the compressible members of the system or changing the orientation of the compressible member relative to the torque beam or beams.